PROJECT SUMMARY Use of public transit has been associated with increased physical activity, and considered a promising approach to reducing the risk of obesity and other age-related chronic conditions such as cancer, diabetes, and heart disease. However, little is known about the physical activity impacts of the increasingly popular Bus Rapid Transit (BRT) which combines the capacity, speed, and reliability of rail transit with the flexibility and cost advantage of a conventional bus system. Further, research is lacking about impacts of transit-oriented multilevel interventions (TOMI) that simultaneously consider multiple synergetic strategies to promote physical activity. This timely natural-experimental study uses a pre-post (opening of new BRT corridors in El Paso, Texas, fall 2018), case- comparison design to examine the causal impact of BRT and other supporting TOMI strategies on residents? physical activity. The study involves 750 exposed (living within 0.5 miles from a new BRT station) and 500 non-exposed (living beyond 1 mile from any BRT stations) adult participants who live in the city and do not meet weekly physical activity recommendations (150+ minutes of moderate-to-vigorous PA) at baseline. The specific aims of this proposed study are to (1) determine physical activity impacts of BRT; (2) examine physical activity impacts of additional TOMI strategies, including education (lifting the knowledge barrier by offering a smartphone app and training to assist transit trip scheduling and to enhance knowledge about using BRT and BRT-reachable physical activity resources) and cost (lifting the financial barrier to transit use by executing an introductory free-fare strategy); and (3) explore benefits and costs of BRT implementation, and barriers and facilitators of BRT use. There will be three waves of data collection in spring 2018, spring 2019, and spring 2021, respectively. The multidisciplinary team (experts from urban planning, transportation, public health, statistics and disparities research) proposes many innovative policy, theoretical and methodological advances to understand the obesity reduction roles of service-oriented environmental interventions. These include a) conceptualization of multi-level factors influencing and strategies for modifying transit use, b) inclusion of multiple case-comparisons, c) application of relevant methodological approaches more commonly used in other research queries, and d) a citizen science approach for more contextual understanding of the PA-transit relationship. Its strong connection with the local communities and stakeholders and substantial record of research collaboration ensure an effective execution of the proposed research. At the end of the proposed study, the researchers expect to identify the physical activity impact of BRT and other TOMI strategies, examine the benefits and costs of BRT implementation, and reveal barriers and facilitators of BRT use.